Of the states that opted in after the standards were introduced in 2010 — 45 plus the District of Columbia — only eight have moved to repeal the standards, largely due to political pressure from those who saw Common Core as infringing on local control, according to Abt, a research and consulting firm. In Oklahoma, Gov. Mary Fallin signed a bill to repeal the standards in 2014 less than six months after defending them in a speech. She said Common Core had become too divisive.

Twenty-one other states have made or are making revisions — mostly minor ones — to the guidelines. Illinois kept the wording while changing the name. In April, North Dakota approved new guidelines "written by North Dakotans, for North Dakotans," but some educators said they were quite similar to Common Core. Earlier this month, New York moved to revise the standards after parents protested new tests aligned to Common Core, but much of the structure has been kept.

"The core of the Common Core remains in almost every state that adopted them," said Mike Petrilli, president of the conservative Thomas B. Fordham Institute.

Launched in 2010 by a bipartisan group of governors and state education chiefs, Common Core sought to bring scholastic standards to the same high level nationwide. The standards quickly became controversial when the Obama administration offered states federal dollars to nudge them to adopt it. States' rights activists cried foul, saying the effort undermined local control. Meanwhile, some teachers criticized the standards as confusing and out of synch with students' needs, while others feared that non-fiction would crowd out the works of Shakespeare.

President Donald Trump and Education Secretary Betsy DeVos spoke out against the standards, but the issue has been largely out of their hands. A 2015 law prohibits the federal government from promoting any set of standards, including Common Core.

A national survey by Education Next, a journal published by Harvard's Kennedy School and Stanford University, found that support for nationwide academic standards rose over the past two years, as long as the name Common Core was not used.

Measuring the direct impact of Common Core is difficult. A study last year by the Brown Center on Education Policy with the Brookings Institution showed that adopters of Common Core initially outperformed their peers, but those effects faded. It's also unclear if the gains were caused specifically by Common Core.

"I think it was much ado about nothing," said Tom Loveless, the author of the report. "It has some good elements, some bad elements. Common Core nets out to be a non-event in terms of raising student achievement."

Petrilli, who advocated for Common Core, is convinced the standards resulted in more rigor and better tests.

"We are now following a much better recipe for student achievement, but the cake is still being baked, so we don't yet know if it's going to taste as good as we hope," Petrilli said.

In the District of Columbia, traditional public schools saw a 7 percent gain in the number of students proficient in English and 6.5 percent gain in math since 2015, when the Common Core standards were fully implemented.

Eric Bethel, principal at Turner Elementary School, says the new guidelines push students to learn "not only the how, but also the why behind the mathematics."

"Students are learning more and what's expected of them is much more rigorous than before," Bethel told AP. As he walked around the school, a walkie-talkie in hand, wide-eyed kindergarteners strolled slowly down a hallway in a neat line, while older students ran around laughing.

Under Common Core, first-grade teacher Amancia Hanna reads her students more non-fiction books than fairy tales and says they find it easier to relate to real-life characters and enjoy reading more.

"That helps them persevere and they see a real person doing it," said Hanna. "Whereas in Cinderella, there is magic, there is fairy tale, you are waiting for somebody to come along and fix this problem for you."

One of Hanna's students, Zakai Winchester, 6, reflected on a lesson he learned from reading. "You should be kind to others and be nice to your friends — you have to listen to each other," he said.

Hanna says Common Core provides instructors with the necessary structure and guidance, which is especially important for new teachers. She said it also seeks to give all students an equal shot.

"I don't care if you are in Minneapolis, I don't care if you are in New York, Florida, wherever you may be — every child deserves that same, equal excellent education and opportunity and I think that the Common Core provides that for all students across the board," Hanna said.

Others disagree. Kristen Brodie, an elementary school teacher in Houston, says the new standards are too rigorous and require analytical skills that young children may not be ready for. She also believes that non-fiction should be introduced in later grades.